A conventional image signal cancel-type heterodyne reception method is such as shown in FIG. 16. That is, from high-frequency signal received by an antenna etc., a signal having a necessary frequency band is taken out by a band-pass filter 41, amplified by a high-frequency amplifier 31, and supplied to mixers 21a and 21b. A first local oscillator 11 oscillates a signal for converting the received high-frequency signal into an intermediate-frequency signal, which oscillated signal is converted by a phase shifter 51 into two-phase signals whose phases are shifted by 90° from each other, which two signals are supplied to the mixers 21a and 21b respectively. The mixers 21a and 21b mix the amplified high-frequency signal and the respective two-phase signals output from the phase shifter 51, so that signals whose frequencies are differences between the frequencies of these signals respectively are taken out as two-phase signals. Output signals of the mixers 21a and 21b are input to band-pass filters 42a 42b respectively, which only a signal desired to be received and its image signal pass through as intermediate-frequency amplifier input signals 94a and 94b. 
The intermediate-frequency amplifier input signals 94a and 94b are amplified by intermediate-frequency amplifiers 32a and 32b to generate intermediate-frequency amplifier output signals 95a and 95b, respectively. The intermediate-frequency amplifier output signals 95a and 95b are modulated at a modulator 53 by using two-phase local oscillator output signals 92a and 92b output from a second local oscillator 13 to cancel the image signal, thus providing base-band signals 96a and 96b for the desired receive signal. The base-band signals 96a and 96b are input to a demodulator 61, where a digital signal is demodulated.
An image signal cancel-type heterodyne reception method is referred to also as a low-IF method and has a merit as a heterodyne method and such an additional merit that the band-pass filters 42a and 42b, which are an intermediate-frequency filter, can be realized easily especially from a viewpoint of downsizing. In the image signal cancel-type heterodyne reception method, it is necessary to amplify each of the intermediate-frequency amplifier input signals 94a and 94b, which are two-phase intermediate frequency signals, that have been amplified by the different amplifiers 32a and 32b conventionally.
However, in a conventional image signal cancel-type heterodyne reception method, it is necessary to use a variable-gain amplifier as each of the amplifiers 32a and 32b, which are an intermediate-frequency amplifier, so that when two-phase intermediate-frequency signals are amplified by the different amplifiers 32a and 32b, it has been difficult to make accurately coincident with each other gains of the amplifiers 32a and 32b, which are two variable-gain amplifiers respectively. Because of this, in the conventional image signal cancel-type heterodyne reception method, it has been difficult to realize a high image signal cancellation ratio.
Further, a conventional direct conversion orthogonal frequency division multiplexing reception method is such as shown in FIG. 17. That is, from high-frequency signal received by an antenna etc., a signal having a necessary frequency band is taken out by a band-pass filter 41, amplified by a high-frequency amplifier 31, and supplied to mixers 21a and 21b. A first local oscillator 11 oscillates a signal for converting the received high-frequency signal into a base-band signal, which oscillated signal is converted by a phase shifter 51 into two-phase signals whose phases are shifted by 90° from each other, which two signals are supplied to the mixers 21a and 21b respectively. The mixers 21a and 21b mix the amplified high-frequency signal and the two-phase signals output from the phase shifter 51 respectively, so that the base-band signals are taken out as two-phase signals. Output signals of the mixers 21a and 21b are input to band-pass filters 42a 42b, which only a signal having a desired band signal passes through, thus providing base-band signals 98a and 98b. 
The base-band signals 98a and 98b are amplified by the amplifiers 32a and 32b to generate two-phase base-band output signals 90a and 90b, respectively. The base-band output signals 90a and 90b undergo sampling and FFT operations at fast-Fourier transform operator (hereinafter abbreviated as FFT operator) 62. An output of the FFT operator 62 is sent to a demodulator 64, which outputs a decided symbol as output data.
A direct conversion orthogonal frequency division multiplexing reception method has a merit that a receiving set can be downsized easily. In the direct conversion orthogonal frequency division multiplexing reception method, it is necessary to amplify two-phase base-band signals differently from each other, which signals have been amplified by the different amplifiers 32a and 32b conventionally.
In the direct conversion orthogonal frequency division multiplexing reception method, it is necessary to use a variable-gain amplifier as each of the amplifiers 32a and 32b, which are a base-band amplifier, so that when two-phase base-band signals are amplified by the different amplifiers 32a and 32b, it has not been so easy to make accurately coincident with each other gains of the amplifiers 32a and 32b, which are two variable-gain amplifiers respectively. Such non-coincidence in gain causes interference between sub-carriers when a signal modulated by orthogonal frequency division multiplexing (hereinafter abbreviated as OFDM) is received, so that it has been necessary and troublesome to make these gains uniform to some extent. Further, a non-coincident error between these gains has deteriorated non-interference between the sub-carriers.
This phenomenon is described as follows. FIG. 17 shows a configuration of a conventional direct conversion orthogonal frequency division multiplexing reception method. A high-frequency signal modulated by OFDM is converted by mixers 21a and 21b into base-band signals 98a and 98b respectively. It is supposed that a value of a signal modulated for a sub-carrier having frequency (fc+f1) is sa and that of a signal modulated for a sub-carrier having frequency (fc−f1) is sb. Note that sa and sb are a complex number. Frequency-f1 components contained in the base-band signals 98a and 98b are given by the following equation 1 by using appropriate complex numbers pa and pb respectively.Re{p a*s a+p b*s b}+j*Im{p a*s a−p b*s b}Re{p a*s a−p b*s b}−j*Im{p a*s a+p b*s b}  [Equation 1]
In Equation 1, j indicates a purely imaginary number and * indicates multiplication, which holds true also in the following. Further, Re and Im indicate a real part and an imaginary part in { } respectively, which holds true also in the following.
If phasing occurs at the time of high-frequency signal reception, values of the complex numbers pa and pb change. In some cases, either one of these values is reduced extremely. Supposing gains of amplifiers 32a and 32b to be ga and gb (both of which are a real number) respectively, components of (fc+f1) and (fc−f1) calculated by an FFT operator 62 are represented by the following equation 2:(g a+g b)*p a*s a+(g a−g b)*p b*s b, (g a−g b)*p a*s a+(g a+g b)*p b*s b  [Equation 2]
Therefore, if values of ga and gb can be made uniform accurately, it is possible to reproduce in a non-interfering manner the signal modulated for the sub-carrier having frequency (fc+f1) and the signal modulated for the sub-carrier having frequency (fc−f1). However, if the values ga and gb have a deviance, interference occurs to make it impossible to separate these signals from each other accurately.